Drive system for a set of machines

ABSTRACT

The invention relates to a drive system powering a group of machines ( 2, 3, 4 ) each fitted with a rectifying unit ( 6 ), the inputs ( 7 ) of the control devices ( 8 ) of the machine&#39; drive motors being interconnected by an electrical bus ( 14 ) which implements a power exchange.

[0001] The present invention relates to a drive system for a group ofmachines each equipped with a drive motor connected by control devicesto a DC power source.

[0002] Applying DC power to the drive motor(s) of a machine, forinstance a weaving machine, is known. In this procedure AC power isconverted by a rectifying unit of the particular machine into DC. ThisDC is applied by controlled switching units to the weaving machine'sdrive motor. Said drive motor preferably shall be a switched reluctancemotor. Preferably such a weaving machine also contains a capacitiveenergy buffer connected to the output of the rectifying unit and to theinput of the switching units. As a result, the power output beyond therectifying unit may remain nearly constant even when the power appliedto the weaving machine's main drive motor varies. The power applied tosaid main drive motor of a weaving machine varies according to aperiodic motion of said weaving machine because it contains componentsthat are moved in one or the other direction at predetermined times.

[0003] The above described drive system meets requirements for weaving.However it is less than desirable for electrically decelerating theweaving machine's main drive motor. For example, the main drive motormust be decelerated to reduce its speed during weaving or to stop it. Insuch a case the energy buffer must store the energy released byelectrically decelerating the main motor. Therefore an energy buffer ofhigh capacity and/or ability to tolerate high voltages will be required.

[0004] As regards rapidly operating weaving machines, it is nearlyimpossible to store the total energy released during deceleration intoan energy buffer. Either an energy buffer of very large capacity wouldbe needed, or the energy buffer's voltage would be too high. To precludeexcessively high energy buffer voltages, it is known in the state of theart to couple a resistor in parallel with the energy buffer when saidbuffer's voltage becomes excessively high, whereby energy is removedfrom said buffer and converted into heat in said resistor. When the maindrive motor of a weaving machine must be frequently decelerated, therewill be danger that the resistor temperature will become excessive.Moreover the heat dissipated by such a resistor must be absorbed byair-conditioning equipment in the weaving room. This aspect againrequires expenditure of relative large amounts of energy.

[0005] The objective of the present invention is to improve a drivesystem of the above cited kind.

[0006] This goal is attained in that the inputs of the control devicesof the drive motors of the group of machines are interconnected byelectric lines in order to carry out power swapping.

[0007] The drive system of the invention offers the advantage that theportion of the energy which is released during deceleration by one ofthe machines of a group may be utilized by another machine in saidgroup. In this case any installed energy buffer need absorb less energyand/or any resistor used need not be switched onto said buffer.

[0008] In a preferred embodiment of the invention, each machine isfitted with a rectifying unit mounted between an AC power source and theinputs of the particular control devices of said machines. The inputs tothe control devices are interconnected, and the rectifying units maycooperate to apply that power, for instance, required to start or toaccelerate one of the machines.

[0009] In another preferred embodiment of the invention, one energybuffer is allocated to the inputs of the control devices of eachmachine. In this way the size of the individual energy buffers may bereduced. Using energy buffers of lesser capacity offers the advantagethat these shall contain fewer pollutants. Because the energy buffers ofthe individual machines may swap energy among one other, they operate inthe form of the sum of their capacities. As a consequence of beingconnected to one another, the total capacity of all energy buffers alsomay be reduced. Furthermore the interconnection of the energy buffersallows drawing on the energy stored in each of them to start oraccelerate a machine. In the latter case the rectifying units are notrequired to apply the full power needed to start or accelerate amachine. Also, using one rectifying unit for each machine, it becomesfeasible to keep the power substantially constant from each rectifyingunit even when only a smaller energy buffer is used per machine.

[0010] In yet another embodiment of the invention, each machine iscombined with a resistor connected by switching units to the input ofits respective control device and/or its respective energy buffer. Whenenergy must be dissipated as heat, this heat can spread over theindividual, switched-on resistors.

[0011] In another embodiment of the present invention, one jointresistor is allocated to a group of machines and is connected byswitching units to the inputs of the control means. Said single resistormay be installed at a remote location, for instance outside the weavingroom. In this manner the heat dissipated by this resistor need not beabsorbed by the weaving room's air-conditioning equipment.

[0012] In yet another embodiment of the present invention, one jointrectifying unit is mounted between an AC source and the inputs of thecontrol devices of the machines. In this design the power may be appliedin part or in whole through the joint rectifying unit whichillustratively converts AC into DC with very high efficiency.

[0013] In yet another embodiment of the present invention, an inverteris mounted between control devices of the machines of a group and an ACpower source. This inverter converting DC into AC allows feeding theenergy recovered during deceleration back into the AC power source.While a single inverter suffices for one group of machines, the invertermay be selected as a more elaborate and correspondingly costlierinverter for recuperating said energy instead of converting it into heatby means of simpler and more economical resistors.

[0014] In still another embodiment of the present invention, the inputsof the control devices of the group's machines cooperate with one jointenergy buffer.

[0015] Preferably the rectifying unit(s) shall each be fitted with asemiconductor forming a DC current at a defined source voltage.

[0016] In a preferred embodiment of the present invention, the group'smachines are weaving machines of which the main drive shafts preferablyare each directly coupled to the associated drive shafts of the drivemotors.

[0017] Further features and advantages of the present invention areelucidated in the description below and in relation to the illustrativeembodiments shown ion the drawings.

[0018]FIG. 1 shows a group of weaving machines equipped with a drivesystem of the invention, and

[0019] FIGS. 2-5 show variants of the drive system of the inventionapplied to groups of machines.

[0020] The drive system 1 of FIG. 1 electrically powers a group ofmachines 2, 3 and 4 from an AC power source 5. Illustratively the powersource 5 is a conventional 380-volt power line at 50 Hz frequency. Arectifying unit 6 is allocated to each machine 2, 3 and 4 converting theAC from the power source 5 into DC. The rectifying units 6 each areconnected to the inputs 7 of control devices 8 which apply DC to theparticular drive motors 9 of the machines 2, 3 and 4. Each machine 2, 3and 4 contains at least one component 10 driven in periodic motion, thatis, moving in one direction or the other at a given time or being raisedor lowered at a given time. The electric drive motor 9 of each of themachines 2, 3 and 4 is correspondingly driven into periodic motion inthat appropriately power having a periodic time-function shall beapplied in a controlled manner by means of the control devices 8 to thedrive motor(s) 9. In particular the time-function of applied power iscontrolled in a manner such that the torque will be constant.

[0021] In this embodiment the drive motor 9 is a switchable reluctancemotor and as a result the control devices 8 each are a switching unit.Each machine 2, 3, 4 is fitted with a control unit 11 applying to thecontrol devices 8 (switching units) certain control parameters retrievedfrom a memory whereby the power is applied in periodic manner to thereluctance motor 9. In this process the switchable reluctance motors 9are controlled according to the machine angular positions in a motionsuch that, by means of the control devices 8 (switching units),predetermined windings of the switchable reluctance motor 9 shall becoupled during a predetermined time interval to the output of therectifying unit 6. The above term “motion” denotes the change in angularposition of the switchable reluctance motor 9. In particular this motionis matched to the natural motion of the machine's components.

[0022] In the shown embodiment, the machines 2, 3 and 4 each are fittedwith an angular-position detector 12 determining the angular position ofthe main drive shaft of the particular machine 2, 3 and 4. Theseangular-position detectors 12 of each machine 2, 3 and 4 are coupled tothe respective control units 11. In this manner the control devices 8(switching units) of each machine 2, 3 and 4 can be actuated as afunction of the signal from the associated angular-position detector 12displaying the angular position of the particular machine 2, 3 and 4.Also, it is possible to determine the angular positions of the machines2, 3 and 4 by determining the angular positions of the respective drivemotors 9. As shown in FIG. 1, the control units 11 of the particularmachines 2, 3 and 4 also may be connected to a central control unitwhich for instance is set up remotely from the machines 2, 3 and 4 andwhich is connected by a network link with the control units 11 of theindividual machines.

[0023] The patent document WO 98/31856 discloses a drive motor of whichthe drive shaft is directly connected to or even is integral with theweaving machine's main drive shaft. The patent document WO 99/27426discloses how such a drive motor is powered into a specific motion,namely the power applied to this drive motor is controlled as a functionof the angular position of said machine. This driving mode is preferredalso with respect to the machines of a group that are driven by thedrive system of the invention. For these reasons the contents of thepatent document WO 99/27426 are hereby declared to be part of thepresent application.

[0024] The inputs 7 of the control devices 8 and hence the outputs ofthe individual rectifying units 6 of the group of machines 2, 3 and 4are interconnected by an electric line 14, as a result of which DC canflow between the group's machines 2, 3 and 4 and also may be swapped.Therefore the DC power of one of the rectifying units 6 may pass intothe individual machines 2, 3 and 4 of the said group.

[0025] In a preferred embodiment of the invention, each rectifying unit6 comprises a number of semiconductors which may or may not becontrolled, for instance a number of diodes which convert AC into DCwith a defined power source voltage. To avoid that one of the rectifyingunits 6 be excessively loaded, advantageously rectifying units 6 areused that will supply DC of substantially the same voltage. Thereforeidentical rectifying units 6 will be preferably used for the individualmachines 2, 3, 4.

[0026] The electric line 14 shall be of sufficient diameter andtherefore have sufficiently low impedance so that the power may betransmitted in near lossless manner. With respect to weaving machines,such a line 14 shall supply a power of at least 3 kW without beingsignificantly and constantly heated by that transmission. Illustrativelylines of copper of several mm in diameters are appropriate.

[0027] In the embodiment of FIG. 1, each machine 2, 3 and 4 contains anelectrical energy buffer 15 mounted between the particular output of therectifying unit 6 and the input 7 of the associated control device 8.Each of said buffers 15 illustratively is in the form of a capacitorwhich may store and release energy. The energy contained in each energybuffer 15 may be fed to one of the drive motors 9 of one of the machines2, 3 or 4. The energy released when decelerating a drive motor 9 of oneof the machines 2, 3 or 4 also may be fed to one of the energy buffers15 still able to accept it. This energy storage is not restricted to oneenergy buffer mounted at one of the particular machines 2, 3 or 4.Consequently any one of the machines 2, 3 or 4 when required to applypeak power may draw energy from the energy buffers 15 and furthermorefrom the rectifying units 6 of each of the other machines.

[0028] The energy released during braking or during deceleration of aparticular machine may be fed to another machine of the same group, as aresult of which the energy buffer(s) 15 are not required to reabsorb theentirety of the said released energy and/or so that additional resistorsdissipating energy into heat will not be needed. This feature isappropriate foremost as regards weaving machines of which theoperational rate must be periodically reduced according to a givenpattern being woven. Illustratively such shall be the case when weavingin several colors, whereby a given filling must be woven at a lowerspeed. The energy stored in the energy buffers of such weaving machinesmust also be available in order to raise again the operational speed ofthe weaving machine. As regards a weaving machine of which theoperational speed varies according to a given pattern, for instancebetween 1,200 and 900 picks a minute, approximately 3 joules arereleased in deceleration. This released energy is partly stored in theenergy buffers 15 and is partly absorbed by the other machines.

[0029] The drive system of the invention only rarely is susceptible tothe need of converting released energy into heat by connection to aresistor. However such a case may arise if several machines are to bestopped simultaneously. For the sake of safety and as shown in FIG. 2, aresistor 16 is provided for each machine 2, 3 and 4 and is connected byswitching units 17 to the outputs of the rectifying units 6 and to theinputs 7 of the control devices 8. In this manner each resistor 16 isalso connected to the energy buffers 15. The switching units 17 arecontrolled by the central control unit 13. All resistors 16 may beswitched ON in the event the voltage of the energy buffers 15 becomesexcessive. Such a voltage value is measured by a voltmeter 18 connectedto the control unit 13 and to the inputs 7 of the control devices 8.Furthermore temperature sensors hooked up to the control unit 13 may beassociated with the resistors 16. In that case and as a function of thetemperature of each resistor 16, the control unit 13 may switch ON theresistor 16 at the lowest temperature if the voltage across the energybuffers 15 is excessive.

[0030] Only one resistor 19 is allocated to the group of machines 2, 3and 4 in the embodiment mode shown in FIG. 3, and can be coupled by theswitching unit 20 with the inputs 7 of the control devices 8 of saidmachines 2, 3 and 4. Appropriately this single resistor will be mountedoutside the room housing the machines 2, 3 and 4, in particular to avoidloading the air-conditioning equipment for that room. The embodimentmode of FIG. 3 furthermore includes a joint rectifying unit 22 of whichthe output 21 is connected to the line 14 which in turn is connected tothe inputs 7 of the control devices 8.

[0031] The basic design of FIG. 4 corresponds to that of FIG. 1. Howeverit includes furthermore an inverter 23 which upon voltages at the inputs7 of the control devices 8 being reached or exceeded, will convert DCinto AC that shall be fed into the AC power source 5. This inverter 23is configured between the inputs 7 of the control devices 8 and the ACpower source 5. In such a design, the resistors 16 and/or 19 may beeliminated. As regards a drive system 1 of the invention, theeventuality of having to feed power back into the power source 5 isremote. Accordingly a relatively small inverter 23 may be used, that is,one which may be smaller than if each machine 2, 3, 4 were fitted withan inverter and required to feed back energy being released at thatmachine.

[0032] A joint energy buffer 24 in FIG. 4 replaces the previousindividual energy buffers 15 and is connected both to the inputs 7 ofthe control devices 8 and to the outputs of the rectifying units 6.

[0033] The embodiment of FIG. 5 substantially corresponds to that ofFIG. 3. However in this latter embodiment, the machines 2, 3 and 4 arenot fitted with their own rectifying unit 6. Instead a centrally locatedrectifying unit 22 is connected between the AC power source 5 and theline 14. The output 21 of rectifying unit 22 is connected to the line 14connecting the inputs 7 of the control devices 8.

[0034] Obviously the invention is not restricted to a group of threemachines 2, 3, 4. At least two machines are needed. However theinvention's advantages shall be greater the more machines belonging toone group are serviced by the drive system of the invention.

[0035] In the shown and above discussed embodiments, each machine 2, 3,4is fitted with only one drive motor 9. However several drive motors maybe used for each machine to drive specific components of that machine.The power applied from the power source to the individual drive motorsmay be considered equivalent to one equivalent power applied to a singlefictitious drive motor of the particular machine.

[0036] The individual embodiments discussed above also may be combinedwithin the scope of the present invention. Machines other than weavingmachines also are applicable, that are powered and decelerated by adrive motor, for instance compressors equipped with an electric drivemotor.

[0037] As regards the drive systems of FIGS. 1 through 4, the rectifyingunits and energy buffers of each machine may be designed for a physicalsize for an average applied power and for storage of average energy.They need not be designed for storing energy peaks when a machine isbeing decelerated or to supply peak power when starting a machine. Onaccount of such a compact design, the electric efficiency of eachrectifying unit of the group of machines will be improved. The inventionalso allows limiting the fluctuations in the power to be applied by eachrectifying unit, and this feature also improves electrical efficiency.

[0038] The drive system of the present invention is especiallyappropriate for a group of machines of which the central control unit 13contains means driving the electric drive motors 9 of the group machines2, 3 and 4 in periodic motions. In an especially advantageous manner,the periodic motions of the individual machines 2, 3 4 of said groupwill be matched to one another in a manner so as to limit the totalpower applied to the group of machines 2, 3, 4 at a predetermined limit.In that case said value illustratively shall be a maximum value and/or amaximum change of the total applied power. The power applied to thedrive motors 9 of the individual machines 2, 3, 4 can be controlled in away disclosed in the patent document WO 99/27426, wherein additionallythe motions of the individual machines are matched to each other, forinstance by the central control unit 13, for instance beingphase-shifted. This feature can be implemented by controlling the mutualangular positions of the various machines. In other words, theparticular motion of one machine will be matched to the motions of theother machines in a way that the instant at which one machine absorbsmaximum power will not coincide with the instant at which anothermachine of the group also absorbs maximum power. As a result, the powerapplied by each rectifying unit may be kept nearly constant even whenusing a comparatively small energy buffer for each machine.

[0039] The invention offers the further advantage that a single machinetogether with its rectifying unit 6 and any energy buffer 15 and/or anyresistance 16 that might be associated to it will work well per se, but,on account of the line 14 in the group, will operate even moreefficiently. For that purpose and as regards the embodiments of FIGS. 1through 4, not only are lines provided for the AC power source 5 betweenthe individual machines, but also lines 14 for DC.

[0040] The invention also applies to a group of machines that are notdecelerated using electric drive motors. In that case the invention isadvantageous to start a machine, in particular if driven in periodicmotions.

[0041] However the drive system of the invention is especiallyappropriate for weaving machines. It allows improving electricalefficiency of a group of weaving machines and therefore is substantiallyadvantageous for weaving mills.

[0042] The apparatus of the invention is not restricted to the shown anddescribed embodiments. Further modifications may be resorted to withinthe scope of the invention.

1. A drive system (1) for a group of machines (2, 3, 4) each equippedwith a drive motor (9) connected by a control device (8) to a DC powersource, characterized in that the inputs (7) of the control devices (8)of the drive motors (9) of the machines (2, 3, 4) of said group areinterconnected for the purpose of swapping current by electrical lines(14).
 2. Drive system as claimed in claim 1, characterized in that eachmachine (2, 3, 4) contains a rectifying unit (6) disposed between an ACpower source (5) and the input (7) of the respective control device (8)of each said machines.
 3. Drive system as claimed in either of claims 1and 2, characterized in that one energy buffer (15) is associated witheach of the inputs (7) of the control devices (8) of each said machines(2, 3, 4).
 4. Drive system as claimed in one of claims 1 through 3,characterized in that one resistor (16) is associated with each machine(2, 3, 4) and is connected through a switching unit (17) to the input(7) of a respective control device (8) and/or to a respective energybuffer (15).
 5. Drive system as claimed in one of claims 1 through 3,characterized in that a joint resistor (19) is associated with the groupof machines (2, 3, 4) and is connected through a switching unit (20) tothe inputs (7) of the control devices (8) of the machines (2, 3, 4). 6.Drive system as claimed in one of claims 1 through 5, characterized inthat one joint rectifying unit (22) is configured between an AC powersource (5) and the inputs (7) of the control devices (8) of the machines(2, 3, 4) of the group.
 7. Drive system as claimed in one of claims 1through 6, characterized in that an inverter (23) is configured betweenthe control devices (8) of the machines (2, 3, 4) of the group and an ACpower source (5).
 8. Drive system as claimed in one of claims 1 through7, characterized in that one joint energy buffer (24) is allocated tothe inputs (7) of the control devices (8) of the machines (2, 3, 4) ofthe group.
 9. Drive system as claimed in one of claims 1 through 8,characterized in that the rectifying unit(s) (6, 22) are fitted withsemiconductors forming a DC of defined output voltage.
 10. Drive systemas claimed in one of claims 1 through 9, characterized in that thegroup's machines (2, 3, 4) are weaving machines of which preferably themain drive shafts are directly connected to the drive shafts of therespective drive motors (9).